class Solution {//leetcode647——回文子串
public:
    int countSubstrings(string s) {
        int n=s.size();
        vector<vector<bool>> dp(n,vector<bool>(n));
        int ret=0;
        for(int i=n-1;i>=0;i--){
            for(int j=i;j<n;j++){
                if(s[i]==s[j]){
                    if(i==j||i+1==j) dp[i][j]=true;
                    else dp[i][j]=dp[i+1][j-1];
                    if(dp[i][j]==true) ret++;
                }
            }
        }
        return ret;
    }
};